Peter Cumming, 58, killed Glasgow University employee Lynda Brown in their home in Glasgow.
Cumming stabbed his partner of eight years four times in the back last September 1. Yesterday he admitted murdering the mother of two.
The High Court in Glasgow heard that Ms Brown and Cumming had planned a dinner party and invited friends Trevor and Rosemary Clarke.
When Cumming returned after buying ingredients for the meal he claimed that Ms Brown told him she had already eaten and this made him "really angry".
Cumming, who told police he was employed as a chef, said he and Ms Brown had had words and added "something snapped".
He said: "I was behind her in the bedroom and I had the knife and I don't know where it came from, I don't know. I was out of control. It's just not like me, I am so in control. I need to keep things in control."
Cumming alleged that Ms Brown reacted to his anger by goading him and said he picked up a large kitchen knife and plunged it into her. He told police that 5ft 3in Ms Brown had not attacked him.
Advocate depute Andrew Miller, prosecuting, said a post-mortem examination revealed she had been stabbed four times in the back.
Defence QC Gordon Jackson said: "It has always been his position that he was willing to plead guilty to murder."
Cumming will be sentenced next month.